1. Technical Field
The present invention relates generally to a reflection-type liquid crystal display apparatus capable of full-color display. Particularly, the present invention relates to a reflection-type liquid crystal display apparatus capable of full-color display without using any color filters, and to a manufacturing method thereof.
2. Description of Related Art
As for a reflection-type liquid crystal display apparatus capable of full-color display, various structures are well known. FIG. 10 shows an example of a reflection-type liquid crystal full-color display apparatus. In the example shown in FIG. 10, a conventional reflection-type liquid crystal display apparatus 51 is constructed by disposing a color filter 53 adapted to let only light of any one of R, G and B pass through a pixel portion, a transparent electrode 54 made of ITO or the like, a liquid crystal 55, and a metal electrode 56 to be used as a reflector, which are provided in this order from the upper side in the drawing between two glass substrate, the upper 52-1 and the lower 52-2. In an actual case, in addition to the elements shown in FIG. 10, a polarizer, a spacer and the like are included. But such elements are omitted in the description because of no direct relation to the present invention.
In the case of the foregoing conventional reflection-type liquid crystal display apparatus, light passes through the color filter 53 twice, i.e., at the time of coming in and going out. Assuming that the incident light intensity is Iin; outgoing light intensity is Iout; transmissivity of the color filter is 53 Tc; the intensity of the reflector is RM; and a constant for others is k, then the relation of these is expressed as follows:
Iout=kTc2RMIinxe2x80x83xe2x80x83(1)
Since the light transmissivity Tc of the single color filter 53 is low, a great reduction occurs in brightness of the reflection-type liquid crystal display apparatus. Therefore, in the foregoing conventional reflection-type liquid crystal display apparatus, the quantity of light that results is inadequate, making it impossible to have full-color display with sufficient brightness.
In order to solve the foregoing problem, a reflection-type liquid crystal apparatus using a color filter of two colors has been presented. This apparatus uses, as a color filter, not three primary colors of R, G and B but two colors of purplish red (=red (R)+blue (B)), and green (G). The use of the two colors instead of the three primary colors enables a transmission spectrum of the color filter to be widened, which can provide better brightness. However, the use of the two colors instead of the three primary colors makes it impossible to produce a full-color display. In addition, because of the use of the color filters, although only the two colors are used, the problem of a reduction in brightness still remains to be solved.
As a method of using no color filters, a reflection-type liquid crystal display apparatus of an ECB system has been presented. This apparatus is a system adapted to display colors by changing a voltage applied to a liquid crystal layer to cause a change in the inclination of liquid crystal molecules, and detecting a resulting change in the birefringence of the liquid crystal layer by a pair of polarizers. In other words, since the wavelength of a reflected light is controlled by an applied voltage, the necessity of a color filter is eliminated for providing better brightness. With this system, however, only spectral light is emitted, and the range of control by a voltage is narrow. Thus, only five colors of white, black, blue, green and red can be expressed.
Japanese Patent Laid-Open No. 7-175079 discloses a liquid crystal display apparatus, which includes a reflective liquid crystal layer adapted to reflect only a circular polarized light in the particular direction of a specified wavelength through cholesteric liquid crystal. Accordingly, it is possible to provide a liquid crystal display having high light utilization efficiency and being capable of vivid display without using any color filters or polarizers. However, there have been problems including the inability to produce a gray scale display and a drastic color change with a viewing angle. Consequently, the foregoing liquid crystal display has been used only as a fixed device.
Further, Japanese Patent Laid-Open No. 7-175079 discloses a reflection-type color filter having a multilayer interference film made of a dielectric multilayer film, and a liquid crystal display using the same. Accordingly, it is possible to provide a reflection-type color liquid crystal display capable of display with brightness sufficient for a practical purpose without using any reflectors or color filters. However, there have been problems including much time and labor for manufacturing the multilayer interference film made of a dielectric multilayer film, and the difficulty of realizing the color liquid display because of costs.
An object of the present invention is to solve the foregoing problems. An object of the present invention is to provide a simply manufactured reflection-type liquid crystal display apparatus capable of securing sufficient brightness because of no use of color filters, also capable of gray scale display and reducing color changes with a viewing angle, and a manufacturing method of the same.
The invention provides a reflection-type liquid crystal display apparatus capable of full-color display. This reflection-type liquid crystal display apparatus comprises a light interference reflector preferably having a grating structure and adapted as a reflector to selectively reflect light only in a particular wavelength range by using light interference. In this case, the light interference reflector is used, the light interference reflector selects incident light, and the reflected light made of only light of receptible wavelength range of R, G and B are respective pixel portions of R, G and B. According to the present invention, the light interference reflector performs the function of a color filter. Thus, it is possible to provide a reflection-type liquid crystal display apparatus capable of securing sufficient brightness, gray scale display and reducing color changes with a viewing angle without using any color filters.
Furthermore, the present invention provides a manufacturing method of a reflection-type liquid crystal display apparatus using a light interference reflector having a grating structure. This method comprises the step of forming a grating structure of a light interference reflector by means of patterning performed by pressing a die on a surface of a metal substrate. Accordingly, one light interference reflector can be formed only by one patterning step performed by pressing the die on the surface of the metal substrate once. Therefore, the light interference reflector, that is to say the reflection-type liquid crystal display apparatus, can be manufactured easily.
These and other aspects, features and advantages of the present invention will be described or become apparent from the following detailed description, which is to be read in connection with the accompanying drawings.